The present invention relates to a hydrogen compressor system, more particularly a hydrogen compressor system suitable for use in a hydrogen refueling station for supplying hydrogen gas to a fuel cell vehicle.
An example of a hydrogen refueling station for supplying hydrogen to a fuel cell vehicle is described in JP-A-2003-194297. The hydrogen refueling station described in JP-A-2003-194297 is a so-called on-site station in which hydrogen is obtained by electrolysis of water. In the on-site station, because pressure of generated hydrogen gas is about 0.6 MPa, a hydrogen compressor system for pressurization is required to supply hydrogen to the fuel cell vehicle. In JP-A-2003-194297, a hydrogen compressor is used to get higher pressure and the compressor is lubricated with water in order to avoid using of oil.
Another example of the system for supplying hydrogen to a fuel cell vehicle is described in JP-A-2005-273811. A hydrogen supplying system described in JP-A-2005-273811 is so-called off-site hydrogen supplying system in which refined hydrogen gas is filled in a hydrogen tank with high pressure to supply the fuel cell vehicle. The system described in JP-A-2005-273811 using the hydrogen tank can supply a required amount of hydrogen to the fuel cell vehicle, regardless of high or low filling load of hydrogen gas.
Because pure hydrogen used in a fuel cell vehicle has wide explosion limit and a large amount of pure hydrogen is likely to be obtained from the nature and also its environmental load is low, pure hydrogen is expected to be an energy source as a substitute for petroleum. However, a low-cost fuel supplying system is required in order to cope with a wide variety of uses.
Thus, in the conventional hydrogen supplying system described in JP-A-2003-194297, a hydrogen generating apparatus using electrolysis of water to obtain hydrogen is used. In the apparatus, because a large amount of time is required from start until a steady state of hydrogen generation is achieved, it is desirable that the apparatus is stopped when hydrogen filling load to the fuel cell vehicle is low in order to reduce operating cost. However, the apparatus is not suitable for start and stop in a short period of time because it has a compressor and the like. As a result, for example when the filling load to the fuel cell vehicle is low, a part of generated hydrogen gas becomes excessive and there is no choice but to wastefully burn the hydrogen gas or emit the hydrogen gas to the atmosphere without any treatment.
On the other hand, in the off-site hydrogen supplying system to the fuel cell vehicle described in JP-A-2005-273811, just a predetermined amount of hydrogen can be supplied regardless of the filling load, but suction pressure of the compressor must be limited to at most about 6 MPa in consideration of the number of compressing stages in the compressor for pressurization. As a result, a larger amount of hydrogen is not supplied to the fuel cell vehicle and remains in the hydrogen tank, so that operating efficiency of the hydrogen tank is reduced.
The present invention is provided in view of the above described disadvantages in the prior arts and it is an object of the present invention to effectively use hydrogen generated by the hydrogen generating apparatus as much as possible. It is another object of the present invention to reduce operating cost of the fuel cell vehicle using hydrogen as a fuel. It is still another object of the present invention to enhance efficiency of the hydrogen refueling station for supplying hydrogen to the fuel cell vehicle. Excessive hydrogen is not exhausted, but recycled as much as possible and the amount of hydrogen which remains in the hydrogen tank is reduced. At least one of the objects is accomplished by the present invention.